1. Field of the Invention
The present invention relates to a light source lighting device and method for lighting a light source to be mounted on a vehicle and, more particularly, to a light source lighting device and method suited for use in a device for lighting an electric bulb such as a head lamp and an auxiliary lamp.
2. Related Art
In the prior art, a head lamp or an auxiliary lamp (e.g., a fog lamp or a spot lamp) to be mounted on an automobile or another vehicle has been widely exemplified by an incandescent bulb or a halogen bulb (as will be referred to as the xe2x80x9cincandescent bulbxe2x80x9d). The vehicle-mounted incandescent bulb is enabled to emit a visible light by applying a direct current from a vehicle-mounted battery to a tungsten filament in a bulb filled with an argon gas, to heat the filament thereby to cause a thermal radiation. The luminance of the head lamp or the auxiliary lamp has direct relation with the visibility for a night drive. It is, therefore, important that a more luminous light emission is obtained by using the battery mounted on the vehicle as a current source.
On the other hand, the lifetime of the incandescent bulb depends on the evaporation rate of the filament. If the incandescent bulb is supplied with an electric current higher than the rated value so as to emit a more luminous light, therefore, the evaporation rate of the filament is accelerated to raise a problem that the lifetime of the incandescent bulb is shortened.
In recent years, on the other hand, a head lamp or an auxiliary lamp using a discharge tube for emitting a light by the discharge phenomenon has been proposed in place of the incandescent bulb. However, the lamp using the discharge tube is far more expensive than that using the incandescent bulb. When this lamp is to be mounted on the vehicle equipped with the lamp of the incandescent bulb, on the other hand, the existing lamp equipment has to be drastically changed.
It is, therefore, an object of the invention to solve the aforementioned problems of the prior art and to provide a lighting device capable of lighting a lamp of an incandescent bulb or the like more luminously with a battery mounted on a vehicle.
Another object of the invention is to provide a lighting device which is freed from shortening the lifetime of the incandescent bulb or the like so much even with the more luminous light emission.
Still another object of the invention is to provide a lighting device which can be additionally mounted on a vehicle having the lamp of the incandescent bulb or the like.
According to an aspect of the invention, there is provided a light source lighting device for lighting a light source to be mounted on a vehicle. The light source lighting device comprises: an inverter for converting a direct current from a vehicle-mounted battery into an alternating current; and current adding means for adding the direct current from the automobile-mounted battery and the alternating current generated by the inverter, to supply the light source with the added electric current.
In the aforementioned construction, the light source is driven by the electric current containing the direct current having alternating current superimposed, thereon so that the luminance of the light source microscopically changes with the period of the alternating current. With the naked eye, however, what is trapped as the light from the light source by the afterimage phenomenon is a light at a luminous time so that it looks more luminous than that at the time when only the direct current is applied.
On the other hand, the invention is preferably constructed to further comprise delay means for delaying an input timing at which the alternating current is supplied to the current adding means.
As a result, the light source is supplied at first with only the direct current and, after a delay of a predetermined time, with the electric current containing the superimposed alternating current. As a result, the electric current to rush into the light source is suppressed not to shorten its lifetime. On the other hand, the luminance stepwise changes so that it is more emphasized by the superimposed electric current.
According to another aspect of the invention, there is provided a light source lighting device comprising: a light source to be mounted on a vehicle; a direct current source; an alternating current source; and current adding means for adding a direct current from the direct current source and an alternating current from the alternating current source, to supply the light source with the added electric current.
In this case, the alternating current source preferably includes an inverter for converting the direct current from the direct current source into an alternating current.
In the aforementioned individual aspects, the direct current to be added in the current adding means is preferably within a voltage range of 10 to 25 V or 20 to 45 V.
On the other hand, the alternating current to be added in the current adding means is preferably within a voltage range of an effective value of 1 to 15 V.
Moreover, the alternating current to be added in the current adding means is preferably within a frequency range of 60 to 100 KHz.
In the aforementioned individual aspects, the vehicle-mounted light source is preferably an incandescent bulb or a halogen bulb.
On the other hand, the vehicle-mounted light source may be an LED.
According to still another aspect of the invention, there is provided a light source lighting method for lighting a light source to be mounted on a vehicle. The lighting method comprises: the step of converting a direct current from a vehicle-mounted battery into an alternating current; the step of adding the direct current from the vehicle-mounted battery and the converted alternating current; and the step of supplying the light source with the added electric cut